As the Doctor and Frobisher exit the TARDIS, they are captured by a robot, placed with the other genetic imperfections and hit with the time cannon. This sends them to prehistoricEarth. The TARDIS is also hit by the cannon and goes with them. The Doctor locates the cube of genetic imperfections and takes it to prevent it from contaminating life on Earth. However, before Frobisher and he can reenter the TARDIS, bodies of dead Hedrons begin to appear. It seems the Hedrons are continuing to use their cannon.

Although he is desperate to prevent the Hedrons from contaminating Earth any further, the Doctor decides that he should pick up Peri in case she can help talk to the Hedrons. Materialising in New York City in the year 1980, the Doctor and Frobisher find Earth controlled by sentient reptiles. Apparently the Hedrons' genetic material has altered the course of life on Earth so that humans never evolved.

The Doctor and Frobisher make a hasty retreat and return to prehistoric Earth to attempt to reverse the damage done by the Hedrons. While the Doctor mulls over the situation, Frobisher decides to grab a bite to eat, but before long a large aquatic dinosaur decides to eat him. Trying to rescue Frobisher, the Doctor grabs the nearest object and hurls it at the dinosaur. However, the nearest object is a sphere containing Hedron genetic material. It smashes open, causing the dinosaur to flee but also irreversibly contaminating prehistoric Earth.

Angry that Frobisher has caused him to further contaminate life on Earth, the Doctor and Frobisher return to Hedron so they can at least destroy the time cannon and prevent it from doing any further damage to the universe. When they arrive on Hedron, however, they find that everyone has died through some terrible cataclysm. They find a recording from one of the last Hedrons and learn that the cause of the destruction was a spaceship that had crashed on the planet, releasing microbes and poisons which the Hedrons had eliminated and to which their immune systems had no defence. As it turns out, the origin of the deadly space ship was none other than the planet Earth. Thus, time had healed its own wounds and the genetic material that the Hedrons had banished from their planet had come back to them with deadly results.

The Doctor destroys the time cannon and Frobisher and he take the TARDIS back to Peri's baseball game. As the Doctor exits the TARDIS he wonders if they will be able to sneak into the game without paying. This seems unlikely, however, as the TARDIS has materialised in the middle of the baseball field, much to the players' confusion.

Although Peri is mentioned several times, she does not actually appear in this story.

The time-placement of Peri's game was not given, but assuming baseball history in the Doctor Who universe does not deviate from the real world on this point it would be in 1957 or earlier, as after that season the Dodgers moved from Brooklyn to Los Angeles.

The Baseball scene in part one contains several minor details which were pointed out to be incorrect in a letter printed in the letters column of DWM 117. The comic called the Dodgers' home stadium "Dodgers Stadium," when the stadium's correct name was "Ebbets Field." Also, there was never an opposing baseball team called the "Redskins" (though there is an American football team by that name). The editorial staff acknowledged these points as errors and responded with an apology.

Another error brought up in the reader's letter was that "the stadium was in Brooklyn, not New York City," but this itself is an error on the reader's part. Both Brooklyn and New York City were correct locations for Ebbets Field, as Brooklyn is a borough within New York City.